Social capital theory provides a framework for analyzing the economic well-being. The purpose of this study is to analyze the age effect of social capital by comparing middle aged and the elderly, as well as to investigate the independent effects of social capital on their subjective economic well-being, respectively. The two concepts of "trust" and "social network" were used to measure the level of social capital. Comparisons between the age groups were made regarding the relationships between social capital and economic well-being of four age groups, including younger middle-aged, older middle-aged, younger elderly, and older elderly. Data from the $2^{nd}$ wave of the Korean Longitudinal Study of Ageing (KLoSA) were used. The final sample for this analysis is 8,406 respondents aged 45~84. The major findings are as follows. First, the level of social capital, trust and social network, is statistically different by age groups. Second, the model fits in the case of model including social capital variables are all larger than their counterparts in the four age groups. Third, social capital is "resource" that can contribute to increasing the subjective economic well-being. Based on the empirical results, implications for welfare policies related with issues of social security for the elderly in Korea are provided.